Fig. 4: MS4A1 is expressed in a previously unidentified subpopulation of OSNs.

A Expression of MS4A1 protein in solitary cells of the main olfactory epithelium. Scale bar, 20 μm. n \(\ge\) 10 mice were tested. B Immunostaining was performed with rabbit polyclonal (green), goat polyclonal (magenta)), and rat monoclonal (cyan) anti-MS4A1 antibodies recognizing different epitopes of the protein. Scale bar, 20 μm. n = 3 mice were tested. C Immunostaining of MS4A1 in the main olfactory epithelia of wildtype and Ms4a1 knockout mice. MS4A1-expressing cells are detected in sections obtained from wildtype (indicated by white arrowheads, left panels) but not Ms4a1 knockout (right panels) mice. Scale bar, 80 μm. n = 4 mice were tested for both wild-type and Ms4a1 knockout mice. D Detection of Ms4a1 mRNA expression (magenta) in anti-MS4A1 antibody labeled cells (green) using combined single-molecule fluorescent in situ hybridization and immunohistochemistry. Scale bar, 20 μm. n = 3 mice were tested. E Determination of whether MS4A1-expressing cells co-express NeuN (neuronal marker, top panels), KI18 (sustentacular cell marker, second panels from the top), KI17 (horizontal basal cell marker, third panels from the top), and NeuroD1 (globose basal cell marker, bottom panels). Scale bar, 20 μm. n = 4–6 mice were tested for each marker. F Expression of CNGA2 (lower panels) but not OMP (upper panels) in MS4A1-expressing cells. Scale bar, 20 μm. n = 4–6 mice were tested for each marker. G MS4A1-expressing cells do not express the genes Gucy1b2, Trpc2, Trpm5, and Pde2a, markers of previously described olfactory subsystems. Scale bar, 20 μm. H MS4A1 is undetected in necklace cells, marked by their expression of Gucy2d (upper panels), and vomeronasal olfactory neurons, marked by their expression of V1rb1 (lower panels). Scale bar, 20 μm. n = 4–6 mice were tested for each marker. I iDISCO immunostaining using antibodies that recognize MS4A1 and VGLUT2, an olfactory glomerular marker, reveals that MS4A1-expressing cells coalesce their axons in the olfactory bulb (left panel). Zoomed-in image of the glomerulus where axons from MS4A1-expressing cells terminate (right panel). n = 3 mice were tested for both wildtype and Ms4a1 knockout mice.